There are various types of color displays that have been in practical use. Thin displays are classified broadly into self-luminous displays, such as PDPs (plasma display panels), and nonluminous displays typified by LCDs (liquid crystal displays). Known as an LCD, which is a nonluminous display, is a transmissive LCD having a backlight disposed on the rear of a liquid crystal panel.
FIG. 41 is a cross-sectional view of a typical structure of a transmissive LCD. The transmissive LCD has a backlight 210 disposed on the rear of a liquid crystal panel 200. The liquid crystal panel 200 is arranged such that a liquid crystal layer 203 is disposed between a pair of transparent substrates 201 and 202, and that polarizers 204 and 205 are provided on the outer sides of the transparent substrates 201 and 202, respectively. Further, a color filter 206 is provided in the liquid crystal panel 200, so that color displays become available.
Although not shown, an electrode layer and an alignment layer are provided inside of the transparent substrates 201 and 202. The amount of light that is transmitted through the liquid crystal panel 200 is controlled for each pixel by controlling the application of voltage to the liquid crystal layer 203. That is, the transmissive LCD controls emitted light from the backlight 210 in such a manner that the amount of light that is transmitted through is controlled at the liquid crystal panel 200, thereby controlling displays.
The backlight 210 emits light that contains wavelengths of three colors RGB necessary for color displays. In combination with the color filter 206, the respective transmittances of red, green, and blue light are adjusted, so that the luminance and hue of each pixel can be arbitrarily set. Used commonly as such a backlight 210 is a white light source such as electroluminescence (EL), a cold-cathode fluorescent lamp (CCFL), or a light-emitting diode (LED).
As shown in FIG. 42, the liquid crystal panel 200 has a plurality of pixels, arranged in a matrix manner, each of which is usually constituted by three subpixels. The subpixels are arranged so as to correspond to red (R), green (G), and blue (B) filter layers of the color filter 206, respectively. Hereinafter, the subpixels will be referred to as R, G, and B subpixels, respectively.
Each of the R, G, and B subpixels selectively transmits, from among the white light emitted from the backlight 210, light falling within the corresponding wavelength band (i.e., red, green, or blue), and absorbs light falling within the other wavelength bands.
In the transmissive LCD thus arranged, the light emitted from the backlight 210 is controlled in such a manner that the amount of light that is transmitted through is controlled at each pixel of the liquid crystal panel 200. This naturally causes some of the light to be absorbed by the liquid crystal panel 200. Further, also in the color filter 206, each of the R, G, and B subpixels absorbs, from among the white light emitted from the backlight 210, light falling outside the corresponding wavelength band. Thus, in an ordinary transmissive LCD, a liquid crystal panel and a color filter absorb so large an amount of light as to reduce the efficiency of use of light emitted from a backlight. Accordingly, the ordinary transmissive LCD suffers from an increase in amount of electricity that is used by the backlight.
Known as a technique for reducing the amount of electricity that is used by a transmissive LCD is a method that involves the use of an active backlight capable of adjusting its light emission luminance in accordance with a displayed image (e.g., Japanese Unexamined Patent Application Publication No. 65531/11999 (Tokukaihei 11-65531 (published on Mar. 9, 1999); hereinafter referred to as “Patent Document 1”).
That is, Patent Document 1 discloses a technique for, by using a luminance-adjustable active backlight to perform display control (luminance control) of an LCD by controlling the transmittance of a liquid crystal panel and the luminance of the active backlight, reducing the amount of electricity that is used by the backlight.
In Patent Document 1, the luminance of the backlight is controlled so as to be identical to the maximum luminance value of an input image (input signal). Further, the transmittance of the liquid crystal panel is adjusted in accordance with the current luminance of the backlight.
At this time, the transmittance of a subpixel, i.e., the maximum value of the input signal becomes 100%. Further, the transmittances of other subpixels are calculated from the backlight value to be not more than 100% each. This makes it possible to darken the backlight when the image is entirely dark, thereby enabling a reduction in the amount of electricity that is used by the backlight.
Thus, in Patent Document 1, the brightness of the backlight is minimized on the basis of the input signal RGB of the input image, and the transmittance of the liquid crystals is increased to the extent that the backlight is darkened. This makes it possible to reduce the amount of light that is absorbed by the liquid crystal panel, thereby enabling a reduction in the amount of electricity that is used by the backlight.
With the foregoing conventional arrangement, the amount of electricity that is used by the backlight can be reduced by reducing the amount of light that is absorbed by the liquid crystal panel. However, the amount of light that is absorbed by the color filter cannot be reduced. If the amount of light that is absorbed by the color filter can be reduced, the amount of electricity that is used can be further reduced.